1. Field of Invention
The invention generally relates to optical communication receivers. The invention more particularly relates to optically pre-amplified receiver nodes.
2. Description of Related Art
In conventional long-haul optical communications applications, the loss between the laser transmitter and the receiver is typically fixed or otherwise substantially invariant. Therefore, a gain block with fixed optical gain serves the purpose of ensuring that the receiver will receive a signal within the receiver""s dynamic range.
In some applications such as metropolitan optical ring networks, however, the loss between the laser transmitter and the receiver often changes due to changes in the span loss or due to channel upgrades. During channel upgrades, extra OADMs (optical add drop multiplexers) are added into the optical path of existing channels, therefore the loss between the transmitter and the receiver changes.
Furthermore, a complete fiber cut, fiber disconnect or other major fault in either a long haul or metro application can cause a loss of signal. As recognized by the inventors, the restoration of the optical signal following a loss of signal event may damage the receiver and/or cause bit errors.
Hence, in these applications a smart pre-amplified receiver is needed that will adapt to changing conditions such as those outlined above.
The invention includes an optical signal converting apparatus for converting an input optical signal to an electrical signal, comprising: a photodetector having an input signal port and an output signal port; an optical amplifier optically coupled to the input signal port of said photodetector, said optical amplifier optically amplifying the input optical signal and outputting an optically amplified signal to the input signal port of said photodetector; a pump optically coupled to said optical amplifier, said pump injecting pumping light into said optical amplifier to provide the optical amplification of the input signal; a power measuring device optically communicating with said optical amplifier, said power measuring device outputting power measurements indicative of the amplified signal""s optical power received by said photodetector; and a controller operatively connected to said pump and to said power measuring device; said controller receiving the power measurements from said power measuring device; and said controller commanding a pump power level output by said pump to perform gain control according to the power measurements received from said power measuring device.
In one construction, the invention may use a receiving device that includes said photodetector and said power measuring device; said controller operatively connected to said pump and to said receiving device; said controller receiving power measurements from said receiving device indicative of the amplified signal""s optical power; and said controller commanding the pump power level output by said pump to perform gain control according to the power measurements received from said receiving device.
Moreover, said optical amplifier may be an erbium doped fiber amplifier.
The optical amplifier may also include a circulator having a first port, a second port, and a third port, wherein the first port of said circulator receives the input optical signal and outputs the received input optical signal to the second port of said circulator; an erbium doped fiber optically communicating with the second port of said circulator; a coupler optically communicating with said erbium doped fiber; an optical selector optically communicating with said coupler; an optical termination optically communicating with said optical selector; said pump optically communicating with said coupler, said pump injecting the pumping light into said erbium fiber via said coupler.
The invention may further include an optical bandpass filter optically communicating with an output of said optical amplifier and the input signal port of said photodetector, said optical bandpass filter having a bandpass including a center wavelength of the input signal.
The invention may also include an OADM receiving a wavelength division multiplexed signal and dropping at least one wavelength onto a drop output port; said optical amplifier optically communicating with the drop output port of said OADM.
Also, the OADM may be operatively connected to a ring or linear network.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.